I don't know why people think "Blaine" was a fan mistranslation. If anything, "Brain" was an SENA mistranslation. The "l" is replace with "r" in Japanese-spoken English words because that's the style. If the original was "Bu-rain-u" or something like that, then it would be natural that the English translation was "Blaine". Again, "Brain" was probably another SENA translation error (right Roxas).

Maybe they can be both correct translations, because in japanese Blaine and Brain sound the same? I don't know japanese, I'm just guessing, but if this is the case then there's no mistake, just a choice they made.

To celebrate the 15th Anniversary of Kingdom Hearts, shirts and acrylic key rings are coming to the Japanese clothing store, PONEYCOMB, located in the shopping mall "109" in Shibuya.

The shirt features Mickey Mouse on the front in his black coat disguise with the word "KING" above him. This shirt comes in a style for women and a style for men. View the shirts below:

There are five different acrylic key rings, each featuring a different character from the series. The characters are Final Form Sora, Roxas in his black coat, Mickey Mouse in his Kingdom Hearts II outfit, Donald Duck, and Goofy. View the key rings below:

UPDATE 1: A release date, as well as prices, for these products have been revealed by Dtimes. These products will be available from PONEYCOMB on April 29, 2017, and the shirts will be available for 3,500 yen ($31.46 USD), while the key rings will be available for 1,500 yen ($13.48 USD).

UPDATE 3: Key rings for Sora/Data-Sora and Chip & Dale have been revealed. View them with the other key rings in the photo gallery above. A couple more Kingdom Hearts shirts have also been revealed to be coming to PONEYCOMB. The shirt designs include one that shows off Timeless River Mickey Mouse on the front and one that shows off the Timeless River world icon on the front and Timeless River Sora on the back. View the shirts in the gallery below:

UPDATE 4: A release date, as well as prices, for these products have been revealed by Dtimes. These products will be available from the PONEYCOMB pop-up shop at Kichijoji Parco 5f for a limited time from June 24, 2017 to August 27, 2017. The Timeless River Mickey shirts will be available for 3,500 yen ($31.46 USD) and the Timeless River Sora shirts will be available for 4,200 yen ($37.75 USD), while the key rings will be available for 1,500 yen ($13.48 USD).

UPDATE 5: Even more Kingdom Hearts shirts and acrylic key rings are coming to PONEYCOMB! Now, the characters Halloween Town Sora, Halloween Town Donald Duck, and Halloween Town Goofy are coming to this line of key rings. There are two new shirts. One of which has a design of Halloween Town Sora and Christmas Town Jack Skellington on the front, and the other shirt has a design of Halloween Town Donald and Goofy on the front. They both come in either black or white.

Both the acrylic key rings and the shirts will be available to pre-order from September 2, 2017 to September 10, 2017. They are planned to ship at the end of September, and regular sales in PONEYCOMB stores are scheduled to begin on September 9, 2017. The key rings will be available to purchase for 1,620 yen ($14.81 USD) each, and the shirts will be available to purchase for 3,780 yen ($34.56 USD) each.